Magnetoelastic force transducers designed in different ways more or less adapted to different measuring purposes are previously known from a plurality of patent specifications. SE-B-151 267 describes such a transducer which comprises a force-subjected magnetic core built up of magnetoelastic sheets and provided with four through-holes for two windings located perpendicular to each other. One of these is an excitation winding which is supplied from an a.c. source for generating a magnetic flux in the core, the other being a measuring winding for sensing the magnitude of the magnetic flux passing through the measuring winding. The principle of measurement is based on the property of magnetic material which means that, when the material is subjected to a mechanical stress, then the permeability is changed in the direction of the stress. The magnitude of the flux which passes through the measuring winding in this way will then depend on the magnitude of the external force applied to the core.
A magnetoelastic transducer with a solid core is described in U.S. Pat. No. 4,802,368. The transducer consists of two identical cylindrical bodies which are held together with the aid of a stud bolt. In an axially and concentrically inner space, there is placed a bobbin with two measuring windings connected in opposition and an excitation winding supplied with alternating current. The interior of the transducer is designed such that, opposite to the respective measuring winding in each of the bodies, a thin cylindrical tubular wall is formed. When the transducer is affected, via the stud bolt, by an externally applied force, a compressive stress arises in one of these tubular walls and a tensile stress in the other. This affects the magnetic conditions such that a signal is obtained from the measuring windings which is proportional to the applied force.
SE-B-300 062 describes a magnetoelastic transducer which is preferably intended to be placed in a circular recess in the magnetostrictive material perpendicular to the direction of stress. The transducer has a cylindrical shape and is provided with a magnetization device connected to an a.c. source as well as a sensing device connected to a measuring device. Both the magnetization device and the sensing device consist of an iron core with a winding applied thereon and the iron cores are each arranged in respective axial planes in the transducer, the two axial planes making an angle of either 90 or 60 degrees with each other.
In certain applications, special requirements are made on the design of the force transducer and on its properties in other respects. These requirements may, for example, be that the force transducer should be insensitive to non-desired forces in the form of lateral loads and to torques. When such requirements have been made, attempts have been made to avoid the problems by enclosing the transducer in load cell housings. These load cell housings often have built-in membrane packages which are weak in the direction of the measuring force but stiff in other directions. This means that only the measuring force is introduced into the transducer. This solution, however, leads to an increased overall height.
As mentioned under the TECHNICAL FIELD, a magnetoelastic transducer according to the invention constitutes a solution to a problem-ridden field where there is a need for a force transducer for very high forces, where lateral loads may occur and where the available space is restricted and, to a certain extent, determined by a special application. Examples of this are hydroelectric generating sets, that is, turbines and generators. These normally have vertically standing shafts with a diameter which may be between 0.6 and 2.0 m. For taking up the vertical force generated by the rotating part, the shaft is provided with a flange resting against a supporting bearing. The shaft is often provided with a guide bearing consisting of a number of bearing segments placed around the periphery of the shaft. To give the bearing segments a certain mobility, these segments are provided, in the centre of the outwardly-facing surface, with a recess for relatively small circular-cylindrical solid bodies--called "studs" within this technical field--which make contact with the surrounding ring or bearing housing of the guide bearing. The studs often have a diameter of 40-60 mm and an axial length of 30-50 mm. One of the circular end surfaces, which faces the bearing segments, is formed such that the contact with the segments consist of an annular, plane surface with an outer diameter corresponding to the diameter of the end surface. The contact of the other circular end surface of the stud with the bearing housing largely occurs within a small region around the centre of the end surface. This is achieved by making this end surface slightly curved in a direction from the periphery and towards the centre.
From several points of view it would be desirable to be able to measure, with force measuring devices, the radial forces arising on the bearing segments of the guide bearing. The problem which arises in that connection is that the force measuring devices must not entail any change of the existing guide bearing constructions.
An example of another application for measurement of compressive force which requires a low overall height is the weighing of containers. It is often desired to mount a load cell into the legs of an already existing container. Since the construction from the beginning did not take into consideration the accomodation of load cells, the space for these are usually minimal.
Other applications of this embodiment of transducers relate to the measurement of tensile force. This transducer can also be used in connection with wire drawing. It is then desired to control the force in the wire to optimize the process while at the same time avoiding, for example, wire breakage.